【单选题】

a variance envelope has been established on a project. the envelope goes from +-30% in r&d to +-5% during manufacturing. the reason for

the change in thickness of the envelope is because:
a. the management reserve has been used up.
b. the accuracy of the estimates in manufacturing are worse than the estimates in r & d.
c. tighter controls are always needed as a project begins to wind down.
d. of the personal desires of the project sponsor.
e. of none of the above